envsetup: export ANDROID_BUILD_TOP earlier

Change-Id: Ia3497f61f4e9aaeeb793cecd3b4f488f0a48181a
diff --git a/envsetup.sh b/envsetup.sh
index 06dadd3..84b06e1 100644
--- a/envsetup.sh
+++ b/envsetup.sh
@@ -324,8 +324,6 @@
 {
     set_lunch_paths
     set_sequence_number
-
-    export ANDROID_BUILD_TOP=$(gettop)
 }
 
 function set_sequence_number()
@@ -1178,4 +1176,4 @@
 source_vendorsetup
 addcompletions
 
-
+export ANDROID_BUILD_TOP=$(gettop)